Ceramic powders are produced for various uses, including specialized mechanical components, coatings for mechanical components, in semiconductor devices (e.g., as High-K dielectric structures), superconducting devices, motion sensors, fuel cells, device packaging, passive electronic components such as capacitors, and more sophisticated energy storage devices and as advanced engineering materials for industries ranging from automobiles to biomedical devices. Numerous techniques exist for the synthesis and fabrication of ceramic powders including solid phase synthesis such as solid-solid diffusion, liquid phase synthesis such as precipitation and co-precipitation, and synthesis using gas phase reactants. Moreover, a host of related fabrication techniques can also be used including: spray drying, spray roasting, metal organic decomposition, freeze drying, sol-gel synthesis, melt solidification, and the like.
In the liquid phase synthesis processes, the metal oxides have been precipitated by the use of oxalic acid and certain of its simple salts. However, various difficulties attend the use of many oxalates, such as unwanted contaminants in the ceramic powder. For example, when alkali or alkaline earth metal oxalates are used, the resulting metal oxide powders may include unacceptable levels of the alkali or alkaline earth metals. As another example, if the oxalate added includes ions such as ammonium (NH4+) that act as a buffer or complexing agent in the solution, control of the pH of the solution may be difficult, resulting in loss of control of product properties.
As the critical dimensions in semiconductor devices continue to be reduced, the impact of even very low levels of trace impurities and even small variations in the atomic and molecular structure of the material become increasingly significant. For example, in high permittivity or high dielectric constant (“Hi-K”) materials, the break-down voltage can become unacceptably low, resulting in the failure of the function of the Hi-K dielectric material, if either or a combination of the levels of trace metal impurities or micro-structure defects become too high. Micro-structure defects can result from a poorly controlled particle size distribution, too large particles, and/or from the presence of impurities, for example. Metal impurities, with or without micro-structure defects, can adversely affect the dielectric properties and breakdown voltage.
In superconductor materials, it is well known that the superconducting properties of the superconductor materials critically depend upon the exact combination of metals in the ceramic powder from which the superconductor material is made. Thus, control of the content of both all component metals and any traces of impurity metals becomes critical to the success or failure of the function of the superconductor.
For at least these reasons, a strong and growing need exists for new methods and materials for use in preparation of the desired ceramic powders, to obtain the ceramic powders having improved properties such as one or more of improved particle size distribution, reduced particle size, reduced metal impurities and improved particle morphology, improved compositional homogeneity, improved control of stoichiometry, improved re-dispersability and enhanced chemical stability.